Method and apparatus for performing path protection for rate-adaptive optics

ABSTRACT

A method and apparatus for performing path protection for rate-adaptive optics is provided. As part of the method, an aggregate input bit stream is received. The aggregate input bit stream is then transmitted using a rate-adaptive optical transceiver when transmitting on a first optical path. When the first optical path has a fault, the aggregate input bit stream is then transmitted on a second optical path using the rate-adaptive optical transceiver and a fixed-rate optical transceiver.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/962,397, filed Aug. 8, 2013. The specification of the presentinvention is substantially the same as that of the parent application.The “Related Application” paragraph has been revised to include aspecific reference to the parent application. The specification of thepresent invention contains no new subject matter.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to optical path protection, andmore specifically to a method and an apparatus for performing opticalpath protection when using rate-adaptive optics.

BACKGROUND

A rate-adaptive optical transceiver is an optical transceiver that isable to adapt its transmittable bit rate in response to changes in thenetwork in which it is operating. Such a transceiver is able to transmitand receive at two or more distinct bit rates. Typically, in order totransmit at a higher bit rate, more advanced modulation techniques areoften needed. The drawback of these more advanced modulation techniquesis that they require a larger optical signal-to-noise ratio (OSNR), andthis reduces the distance over which the signal can be transmitted. Thenet result of this (in overly simplistic terms) is that therate-adaptive optical transceiver is able to transmit at a high bit rateover a short distance, and is able to transmit at a low bit rate over along distance. If a rate-adaptive optical transceiver is transmitting ata high bit rate over a short optical path, and that path later fails sothat the transceiver must now transmit over a longer path in order toget around the failure, then the transceiver may be required to lowerits bit rate in order to transmit over the new distance. At this point,the original transceiver must either drop some of the lower prioritytraffic it is transmitting, or move some of its traffic to anotheroptical transceiver.

SUMMARY

A method and apparatus for performing path protection for rate-adaptiveoptics in accordance with example embodiments of the present inventionis provided. This method employs fixed-rate optics to assistrate-adaptive optics in the presence of optical path failures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1 is an illustration of generalized rate-adaptive opticaltransceiver.

FIG. 2 is a detailed illustration of a first embodiment of arate-adaptive transceiver.

FIG. 3 is a detailed illustration of a second embodiment of arate-adaptive transceiver.

FIG. 4 is a first embodiment of the transmitter portion of an apparatusfor performing path protection for rate-adaptive optics.

FIG. 5 is a first embodiment of the receiver portion of an apparatus forperforming path protection for rate-adaptive optics.

FIG. 6A is a second embodiment of an apparatus for performing pathprotection for rate-adaptive optics.

FIG. 6B is the continuation of the second embodiment of an apparatus forperforming path protection for rate-adaptive optics.

FIG. 7 is a network diagram of a first type of network failure.

FIG. 8 is a network diagram of a second type of network failure.

FIG. 9 is a network diagram of a third type of network failure.

DETAILED DESCRIPTION

A description of example embodiments of the invention follows. FIG. 1shows a block diagram of a generalized rate-adaptive optical transceiver100. The transceiver comprises a transmitter (TX) 110 and a receiver(RX) 130.

The transmitter 110 receives an electrical input data stream at input112, and forwards that input stream to the TX input processor 114. TheTX input processor 114 may reformat the input data, and may add ForwardError Correction bits and perform other user specific function. The TXinput processor 114 then directs the input data to one or more TX rateprocessors 116 a-c. In the rate-adaptive optical transceiver 100, thereare N TX rate processors shown 116 a-c. Each of the N TX rate processors116 a-c is capable of generating an output bit stream at a different bitrate. For example, the TX Rate 1 Processor 116 a may be capable ofgenerating an output bit stream at a higher rate than the TX Rate 2Processor 116 b, while the TX Rate 2 Processor 116 b may be capable ofgenerating an output bit stream at a higher rate than the TX Rate NProcessor 116 c. For these cases the TX Rate 1 Processor 116 a may use afirst modulation format, the TX Rate 2 Processor 116 b may use a secondmodulation format, and the TX Rate N Processor 116 c may use a thirdmodulation format. For example, the first modulation format may be aPAM-16 modulation (16-level Pulse-Amplitude Modulation) format, thesecond modulation format may be a PAM-4 modulation format, and the thirdmodulation format may be a PAM-2 modulation format. The PAM-16modulation format transmits four bits of information per symbol, thePAM-4 modulation format transmits two bits of information per symbol,and the PAM-2 modulation format transmits one bit of information persymbol. Therefore, in this example, if all three TX rate processors 116a-c are transmitting at the same symbol rate, the TX Rate 1 processor116 a (using PAM-16) can transmit at a bit rate that is twice the rateof the TX Rate 2 processor 116 b (using PAM-4), and the TX Rate 2processor 116 b (using PAM-4) can transmit at a bit rate that is twicethe rate of the TX Rate N processor 116 c (using PAM-2). However, for agiven fiber type, since the PAM-16 modulation format requires a higherOSNR to transmit error free than the PAM-4 modulation format, thedistance achieved by the PAM-16 format will generally be less than thedistance achieved by the PAM-4 format. This is due to the fact thatlonger distances require higher amounts of optical amplification, andthis generally lowers the OSNR of a given signal.

Although the previous example discussed the operation of the TX rateprocessors using various PAM-n modulation formats, the TX rateprocessors are not limited to PAM-n modulation formats, and in fact eachTX rate processor may use any implementable modulation format,including, but not limited to Quadrature Phase Shift Keying (QPSK), andvarious Quadrature Amplitude Modulation (QAM) formats (8QAM, 16QAM,etc.). Also, the various rate processors within the rate-adaptiveoptical transceiver need not have the same symbol rate.

A 1 for N selector 118 is used to select between the various bit ratesof the various TX rate processors. For a given optical path, the 1 for Nselector 118 is configured to forward one of the N bit rates to the TXoutput processor 120. The TX output processor may additionally formatthe electrical signal prior to forwarding it to the TX optics 122. TheTX optics 122 uses a laser to convert the electrical signal from theoutput processor 120 to an optical signal of a configurable wavelength(frequency). In addition, the laser can be turned off, so that no lightemits from the output 124 of the rate-adaptive optical transceiver 100.

The receiver 130 receives an optical input data stream at optical input114. The optical input data stream is converted into an electrical datastream by the Receiver (RX) optics 142, and it is then forwarded to theRX input processor 140 for any preliminary processing (equalization,phase recovery, etc.) prior to being forwarded to the 1 to N fan-outcircuitry 138. The 1 to N fan-out circuitry 138 either selectivelyforwards it inputted data to one or more of the plurality of RX rateprocessors 136 a-c, or broadcasts its inputted data to all of the RXrate processors. Each of the N RX rate processors 136 a-c demodulatesthe incoming signal according to its corresponding modulation format,and produces an outgoing bit stream according to is corresponding ratecapabilities. In general, there is a one-to-one matching of each RX rateprocessor 136 a-c to a corresponding TX rate processor 116 a-c.Therefore, for example if TX rate processor 116 a produces a 50 Gbpsdata stream using a PAM-4 format, then the corresponding RX rateprocessor 136 a demodulates its incoming signal using a PAM-4demodulator, and produces a corresponding 50 Gbps data stream. The RXrate processor that processes the corresponding receiver signal forwardsits output data to the RX output processor 134. The RX output processor134 preforms any final processing on the signal (such as FEC decoding,for example), and forwards the resulting electrical signal to its outputport 132.

If the rate-adaptive optical transceiver is operating at a first bitrate r₁, over a first distance d₁, over a first optical path, and thenif a fault occurs on the first optical path such that the transceivermust now transmit over a second optical path over a second distance d₂,wherein d₂>d₁, then the transceiver may need to switch to a second bitrate r₂, wherein r₂<r₁. This is done by selecting a different rateprocessor within the optical transceiver.

FIG. 2 shows a detailed block diagram of a first embodiment of arate-adaptive optical transceiver 200, comprising a transmitter (TX) 210and a receiver (RX) 230. Both the transmitter 210 and the receiver 230may include a variety of integrated circuit devices (ICs), as shown inFIG. 2. Alternatively, the various functions could be consolidated intoa single IC or in some number of ICs less than that shown in FIG. 2. Forexample, both some number of TX rate processors and RX rate processorscould be consolidated into a single IC, and or the TX Mapper and RXMapper functions could be consolidated into a single IC.

The transmitter 210, comprises a group of p input ports 212, a TX mapperIC 211, a TX input processor and distributor IC 214, N number of TX rateprocessor ICs 216 a-b, a 1-for-n selector IC 218, TX optics 222, and anoptical output port 224. Up to p number of input data streams isreceived at the group of p input ports 212. These data streams may bemapped by the TX mapper IC 211 into transport units such as the opticaldata units ODUs defined by ITU-T Recommendation G.709. The TX mapper ICmay further perform such functions as error checking and performancemonitoring. The mapper IC 211 aggregates the group of p input streamsinto one aggregate input bit stream 215, and may further add forwarderror correction bytes to the stream before forwarding the stream 215 tothe TX input processor and distributor IC 214. The TX input processorand distributor IC 214 may further format the aggregate input bit stream215 in accordance to the individual requirements of each TX rateprocessor 216 a-b. Following any further formatting, the TX inputprocessor and distributor IC 214 forwards the “processed” aggregateinput bit stream 215 to one of the N TX rate processor ICs 216 a-b.

The TX rate processor ICs perform the same function as described inreference to the TX rate processors 116 a-c of FIG. 1. A given TX rateprocessor performs any “rate specific” and “modulation specific”processing and formatting required for its specific output bit rate,while mapping the received aggregate input bit stream to its output bitstream. For instance, for a PAM-16 modulation format, the correspondingTX rate processor would need to parse the aggregate input bit streaminto four-bit symbols as part of the processor's functionality. The TXrate processor with the highest output bit rate would be designed totransmit the maximum aggregate bit rate received from the group of pinput ports 212.

Each TX rate processor IC may support m_(i) number of different physicalformats for its output signals. For instance a given TX rate processormay support both a 10 Gbps serial format and a 28 Gbps physical format,each of which may require different serializer/deserializer devices(SERDES) within the IC—resulting in separate pins for the 10 Gbps and 28Gbps signals. If there are N TX rate processor ICs—each with m_(i)number of different physical formats—then the total number of physicaltransmission entities outputted by the group of TX rate processors isequal to: Σ₁ ^(N) m_(i)=n. Therefore, in order to select from n numberof physical transmission entities, a 1-to-n selector IC 218 is required.The 1-to-n selector IC is configured to select and forward the bitstream of the physical transmission entity corresponding to the rateused to transmit the aggregate input bit stream 215 from the transmitter210 of the rate-adaptive optical transceiver. The selected bit stream isthen forwarded from the selector 218 to the TX optics 222—for conversionfrom electrical to optical format—and then outputted on optical output224.

The receiver 230 comprises a group of p output ports 232, an RX mapperIC 231, an RX output processor IC 234, N number of RX rate processor ICs236 a-b, a 1-to-n fan-out IC 238, RX optics 242, and an optical inputport 244. An optical signal is received at input 244, and it isconverted to electrical format by the RX optics 242, and then forwardedto the 1-to-n fan-out IC 238. The fan-out IC 238 is configured toforward its received signal to one of the n physical transmissionentities of the N RX rate processor ICs 236 a-b. If there are N RX rateprocessor ICs—each with m_(i) number of different physical formats—thenthe total number of physical transmission entities outputted by the1-to-n fan-out IC 238 is equal to: Σ₁ ^(N) m_(i)=n. Therefore, in orderto forward to n number of physical transmission entities, a 1-to-nfan-out IC is required. In its simplest form, the 1-to-n fan-out IC 238simply broadcasts its received signal to all n of its outputs. A moresophisticated fan-out IC selectively sends its received signal to one ormore particular outputs, and sends no signal to its other outputs.

The N RX rate processor ICs 236 a-b behave in the same manner as thecorresponding rate RX processors of FIG. 1. A given RX rate processorperforms any “rate specific” and “de-modulation specific” processing andformatting required for its specific input bit rate, while mapping thereceived input bit stream to its output bit stream. The RX rateprocessor with the highest input bit rate would be designed to receivethe maximum aggregate bit rate transmitted to the group of p outputports 232.

The RX output processor and selector IC 234 selects the output streamfrom the RX rate processor that is actively processing the input signalof the receiver, and performs any required formatting of the signal,prior to forwarding the signal to the RX mapper IC 231. The RX mapper IC231 may perform forward error correction on the signal it receives fromthe RX output processor. The signal from the RX output processor may bepartitioned into multiple transport units such as the optical data unitsODUs defined by ITU-T Recommendation G.709. The RX mapper IC de-maps thenative signals from the transport units, and then forwards the de-mappedsignals to the appropriate output ports 232 of the receiver.

FIG. 3 is a detailed block diagram 300 of a second embodiment of arate-adaptive transceiver. It includes a transmitter (TX) block 310 anda receiver block 330. The rate-adaptive optical transceiver 300 isidentical to the rate-adaptive optical transceiver 200 except in regardsto the circuitry residing between the rate processors 216 a-b, 236 a-band the optical input/outputs 224, 244, 324, and 344. In 300, there arej number of TX optical blocks 322 a-b (instead of only one 222), andthere are j number of RX optical blocks 342 a-b (instead of only one242). Each of the j TX optics 322 a-b and RX optics 342 a-b operate overa specific range of rates (or in the simplest case, operate at a singlerate). In order to accommodate the additional optics, a j-for n selectorIC 318 is used (instead of 1-for n selector IC 218), and a j-to-nfan-out IC 338 is used (instead of a 1-to-n fan-out IC 238). Inaddition, a j-to-l optical switch 328 is needed to select from thevarious TX optics before outputting the selected signal to output port324, and a 1-to-j optical switch is needed in order to forward theoptical signal from the input port 344 to the correct RX optics 342 a-b.The adaptive-rate optical transceiver 300 may be used when a single setof optics is not able to support all of the desired rates of thetransceiver.

A variant of the rate-adaptive optical transceiver may include atransceiver that has a single TX optics, but multiple RX optics, or viceversa. A second variant of the rate-adaptive optical transceiver mayinclude a rate-adaptive optical transceiver wherein each of its rateprocessors is paired directly with specific TX and RX optics—thuseliminating the need for a j-for-n selector IC and a j-to-n fan-out IC.

FIG. 4 is a first embodiment of the transmitter portion of an apparatusfor performing path protection for rate-adaptive optics 400. Theapparatus 400 is appropriate to use when protecting paths that begin andend on the same optical fiber. Therefore, the apparatus only requires asingle network (NW) output 426. The transmitter portion of the apparatusfor performing path protection for rate-adaptive optics 400 comprisesone or more rate-adaptive optical transceivers (TX) 410 a-c, at leastone fixed-rate optical transceiver (TX) 456, an optical mux 430, aselector 450, a group of input ports 412 a for each rate adaptiveoptical transceiver (not shown on transceivers 410 b and 410 c), and anoptical output port 426.

Each rate-adaptive optical transceiver (TX) 410 a-c comprises a group ofinputs ports 412 a (only shown for 410 a), a TX mapper function 414(only shown for 410 a), a switch 415 (only shown for 410 a), TX rateprocessors and selector 430 (only shown for 410 a), TX optics 422 (onlyshown for 410 a), an optical output 424 a-c, and a switch output 421a-c. The TX mapper function 411 performs substantially the samefunctions as the TX mapper IC 211, and may be implemented with one ormore ICs. The TX input processor and distribution function 414 performssubstantially the same functions as the TX input processor anddistribution IC 214, and may be implemented with one or more ICs. The TXrate processors and selector function 430 performs substantially thesame functions as the N TX rate processor ICs 216 a-b and the 1-for-nselector IC 218, and may be implemented with one or more ICs. The TXoptics 422 performs the electrical to optical conversion. The electricalswitch 415 provides the ability to configurably send data received from414 to either the TX rate processor and selector 430 or the switchoutput port 421 a.

The at least one fixed-rate optical transceiver (TX) 456 comprises anelectrical input 455, electronics 457, TX optics 458, and an opticaloutput 424 d. An electronic data stream received at input 455 isforwarded to the electronics 457 wherein any required formatting orother processing is performed. The electronics 457 then forwards theprocessed data stream to the TX optics 458, which convert the electricalsignal to an optical signal prior to sending it out its output opticalport 424 d.

Operation of the TX portion of the apparatus 400 is as follows. Therate-adaptive optical transceiver (TX) 410 a receives a set of inputdata streams from its group of input data ports 412 a. The TX mapperfunction maps the input data streams to the appropriate transport unitsand then combines them into one aggregate input bit stream 423. Theaggregate input bit stream may be physically transferred over a singlephysical transmission entity (such as a single differential electricalpair of signals), or it may be physically transferred over a pluralityof physical transmission entities 423, as indicated in FIG. 4. The TXmapper 411 forwards the aggregate input bit stream to the TX inputprocessor 414, wherein some preparation for the rate processors may beperformed, prior to forwarding to the switch 415. When the aggregateinput bit stream 423 is forwarded on a first optical path, the switchmay forward the entire aggregate input bit stream to the TX rateprocessors and selector 430. The TX rate processors and selector 430formats the aggregate input bit stream 423 prior to outputting it to theTX optics 422 using a first transmittable bit rate. The TX optics 422converts the received electrical signal to an optical signal with aunique wavelength (frequency) prior to forwarding the signal out of thetransceiver's output port 424 a. The output port 424 a is opticallyconnected to input port 431 a on the optical mux 430. The optical mux430 is capable of optically multiplexing wavelengths on all of itsinputs 431 a-d into a single wavelength division multiplexed (WDM)signal, after which it outputs this signal on the output port of thetransceiver 426. The optical signal leaving the transceiver my then berouted from the apparatus (the first apparatus) to a second “apparatusfor performing path protection for rate-adaptive optics” via an opticalnetwork connecting the first apparatus to the second apparatus.

The first optical path may be such that the optical transceiver is ableto operate at its highest bit rate, thus allowing the entire aggregateinput bit stream to be transported to the second apparatus using asingle wavelength. If a fault occurs on the first optic optical path,the aggregate input bit stream may need to be routed through the networkon a second optical path. However, conditions associated with the secondoptical path may be such that the rate-adaptive optical transceiver canno longer transmit the entire aggregate input bit stream to the secondapparatus at the same bit rate without causing bit errors. For thiscase, the rate-adaptive optical transceiver (TX) reduces its output bitrate to a second transmittable bit rate in order to achievesubstantially error-free transmission. Once it reduces its output bitrate, the rate-adaptive optical transceiver can no longer transmit theentire aggregate input bit stream 423, and therefore it may now dividethe bit stream into a first portion and a second portion. This isperformed by the switch function 415. The switch function forwards thefirst portion of the aggregate input bit stream 423 to the TX rateprocessors and selector block 430 for transmission out of therate-adaptive optical transceiver at output 424 a, and forwards thesecond portion to its switch output port 421 a. The switch output portis electrically connected to the 1-of-k selector 450 via electrical line425 a. When the fault occurs on the first optical path, the 1-of-kselector 450 is configured to forward the electrical signal received onits input 452 a to its output 454. Since the input 455 to the fixed-rateoptical transceiver 456 is connected to the output 454 of the 1-of-kselector 450, the second portion of the aggregate input bit stream isforwarded to the fixed-rate transceiver. The fixed-rate opticaltransceiver 456 converts the second portion of the aggregate input bitstream to an optical signal while assigning it to a second wavelength(frequency). The fixed rate optical transceiver transmits the secondportion of the aggregate input bit stream using a third transmittablebit rate. The second wavelength is multiplexed along with the firstwavelength from the rate-adaptive optical transceiver by the optical mux430. The output bit rate of the fixed-rate optical transceiver is suchthat it is able to transmit the second portion of the aggregate inputbit stream on the second optical path to the second apparatus withouterror.

The apparatus provides a means of transmitting the aggregate input bitstream out of the apparatus by providing a combined electrical andoptical path from the set of input ports 412 a to the output port 426.The wavelength (frequency) assigned to the optical signal exiting therate-adaptive transceiver is used to guide the wavelength from the firstapparatus to the second apparatus by way of the optical network thatresides between the two apparatuses. Each apparatus resides within anoptical node of the optical network, and there may be one or moreadditional optical nodes between the nodes holding the two apparatuses.Prior to a fault on the first optical path, configuring therate-adaptive optical transceiver to transmit the aggregate input bitstream out of the apparatus using a particular wavelength, provides anoptical identifier for the optical signal as it makes its way from thefirst apparatus to the second apparatus. Each node between the twoapparatuses is configured to route the received wavelength along thefirst optical path by using the frequency of the wavelength as anoptical identifier. Therefore, once each network node between the twoapparatuses is configured correctly, by configuring the opticalfrequency (wavelength) of the optical signal exiting the rate-adaptivetransmitter to a particular optical frequency (wavelength), theapparatus is providing a means to output the wavelength on the firstoptical path.

When the fault (failure) occurs on the first optical path, the opticalsignal carrying the aggregate input bit stream must be “routed” aroundthe fault (failure). In order to do this the optical nodes between thetwo apparatuses may need to be reconfigured in order to direct thewavelength carrying the aggregate input bit stream around the fault(failure). Additionally, the wavelength (frequency) used by the opticalsignal carrying the aggregate input bit stream may need to be changed bythe rate-adaptive optical transceiver 410 a. After the fault occurs, thenetwork is additionally configured to route the optical wavelength usedby the fixed-rate optical transceiver through the optical network fromthe first apparatus to the second apparatus. The optical wavelength(frequency) used by the fixed-rate optical transceiver may alsoconfigurable, so by configuring the wavelength to a particular value,the apparatus provides a means of transmitting the wavelength of thefix-rate optical transceiver on the second optical path. By controllingthe optical wavelength used by the optical signals carrying theaggregate input bit stream, the apparatus provides a means oftransmitting the aggregate input bit stream on the first optical pathand on the second optical path.

In summary, FIG. 4 shows an apparatus comprising a group of one or moreinput ports 412 a with an aggregate input bit stream 423, arate-adaptive optical transceiver 410 a having a first transmittable bitrate and at least a second transmittable bit rate, at least onefixed-rate optical transceiver 456 having a third transmittable bitrate, and a means of transmitting the aggregate input bit stream out ofthe apparatus on a first optical path and on at least a second opticalpath, wherein when transmitting the aggregate input bit stream on thefirst optical path, the rate-adaptive optical transceiver is used, andwherein when transmitting the aggregate input bit stream on the at leastsecond optical path, the rate-adaptive optical transceiver and the atleast one fixed-rate optical transceiver are used.

The aggregate input bit stream is transmitted on the first optical pathas long as there is no fault on the first optical path. For this case,only the rate-adaptive optical transceiver is used to transmit theaggregate input bit stream. As a result of a fault on the first opticalpath, the aggregate input bit stream is transmitted on at least a secondoptical path. For this case, both the rate-adaptive optical transceiverand the fixed-rate optical transceiver are used to transmit theaggregate input bit stream.

For the fault scenario, the optical wavelength generated by thefixed-rate optical transceiver does not necessarily have to take thesame optical path as the wavelength generated by the rate-adaptiveoptical transceiver. It may instead be transmitted on a third opticalpath. Therefore, at a minimum a second optical path may be used, and ata maximum, both a second and third optical path may be used. In eithercase, “at least” a second optical path will be used.

As an optical signal passes through an optical network, the signal willaccumulate noise. This is due to optical amplifiers within the network.The result is that the signal's optical-to-signal-noise-ratio (OSNR)decreases as it passes through an optical network. At some point, thenoise will become large enough such that the signal can no longer betransported through the network substantially error free. This point isoften regarded as the OSNR threshold. The difference between the OSNR ofa signal and its OSNR threshold is often referred to as the signal'sOSNR margin. The larger the OSNR margin is for a given optical signal,the more unlikely it is for the signal to incur bit errors. When therate-adaptive optical transceiver transmits the entire aggregate inputbit stream on the first optical path using a first transmittable bitrate, it may likely be configured to transmit at the lowest possible bitrate for that optical path, as the lowest possible bit rate willtypically provide the largest OSNR margin. When the rate-adaptiveoptical transceiver transmits on the second optical path, therate-adaptive optical transceiver may be capable of transmitting theentire aggregate input bit stream on the second optical path withouterrors while still using the first transmittable bit rate. For thiscase, the fixed-rate optical transceiver is not necessary. However, ifthe second path is such that the rate-adaptive optical transceivercannot transmit the entire aggregate input bit stream on the secondoptical path without errors, using the first transmittable bit rate, itmay need to use a second transmittable bit rate, wherein the secondtransmittable bit rate is less than the first transmittable bit rate.For this case, the rate-adaptive optical transceiver may likely onlytable to transmit a first portion of the aggregate input bit stream, andthe fixed-rate optical transceiver would be needed to transmit thesecond portion of the aggregate input bit stream.

There may be several reasons why the rate may need to change whentransitioning to a new optical path. For instance, the first opticalpath may be shorter than the at least second optical path. Or, thesecond optical path may be noisier than the first optical path. Or, thesecond optical path may have a greater amount of chromatic dispersion(CD) than the first optical path. Or, the second optical path may have agreater amount of polarization mode dispersion (PMD) than the firstoptical path. Or, second optical path may use a different type of fiberthan the first optical path. Or, the second optical path may have somecombination of all of the previous reasons.

For a network built with similar fiber, and using similar opticalequipment throughout, the most common reason for having to lower thetransmittable bit rate may be because the second optical path is longerthan the first optical path. A longer distance path typically requiresadditional optical amplification, leading directly to a lower OSNR.

The simplest rate-adaptive optical transceiver is one that has only twoconfigurable transmittable rates. In one embodiment of a rate-adaptiveoptical transceiver with two configurable transmittable rates, the firsttransmittable bit rate is at least equal to twice the secondtransmittable bit rate. For example, the first transmittable bit ratemay utilize a PAM-4 modulation method at 10 Giga-symbols per second (20Gbps), while the second transmittable bit rate may utilize a PAM-2modulation method at 10 Giga-symbols per second (10 Gbps). For thisexample, the first transmittable bit rate is equal to twice the secondtransmittable bit rate.

The fixed-rate optical transceiver may have a third transmittable bitrate. The third transmittable bit rate will likely be less than thehighest transmittable bit rate of the rate-adaptive optical transceiver.The third transmittable bit rate may be less than the highesttransmittable bit rate of the rate-adaptive optical transceiver, butgreater than the lowest transmittable bit rate of the rate-adaptiveoptical transceiver. The third transmittable bit rate may be equal toone of the transmittable bit rates of the rate-adaptive opticaltransceiver. The third transmittable bit rate may be equal to the lowesttransmittable bit rate of the rate-adaptive optical transceiver. Thethird transmittable bit rate may be lower than the lowest transmittablebit rate of the rate-adaptive optical transceiver.

Given that a given signal format may have a higher percentage ofoverhead bytes than another signal format, instead of comparing raw bitrates (as was done previously), one may compare “payload” bit rates.It's important to consider payload bit rates because some transmissionformats are more efficient than others. For instance, for arate-adaptive optical transceiver with two transmittable bit rates, itsfirst transmittable bit rate may be three times its second transmittablebit rate, but the transmittable payload bit rate of its firsttransmittable bit rate may only be twice the transmittable payload bitrate of its second transmittable bit rate. Since a given opticaltransceiver's main purpose is to transport payloads, a transceiver'spayload transmittable bit rate is all that really matters. Therefore,the invention can be described in terms of payload transmittable bitrates. With that said, FIG. 4 shows an apparatus comprising: a group ofone or more input ports 412 a with an aggregate input bit stream 423, arate-adaptive optical transceiver 410 a having a first payloadtransmittable bit rate and at least a second payload transmittable bitrate, at least one fixed-rate optical transceiver 456 having a thirdpayload transmittable bit rate, and a means of transmitting theaggregate input bit stream out of the apparatus on a first optical pathand on at least a second optical path, wherein when transmitting theaggregate input bit stream on the first optical path, the rate-adaptiveoptical transceiver is used, and wherein when transmitting the aggregateinput bit stream on the at least second optical path, the rate-adaptiveoptical transceiver and the at least one fixed-rate optical transceiverare used.

When the rate-adaptive optical transceiver transmits the entireaggregate input bit stream on the first optical path using a firsttransmittable payload bit rate, it may likely be configured to transmitat the lowest possible transmittable payload bit rate for the firstoptical path, as the lowest possible transmittable payload bit rate willtypically provide the largest OSNR margin. When the rate-adaptiveoptical transceiver transmits on the second optical path, therate-adaptive optical transceiver may be capable of transmitting theentire aggregate input bit stream on the second optical path withouterrors while still using the first transmittable payload bit rate. Forthis case, the fixed-rate optical transceiver is not necessary. However,if the second path is such that the rate-adaptive optical transceivercannot transmit the entire aggregate input bit stream on the secondoptical path without errors, using the first transmittable payload bitrate, it may need to use a second transmittable payload bit rate,wherein the second transmittable payload bit rate is less than the firsttransmittable payload bit rate. For this case, the rate-adaptive opticaltransceiver may likely only table to transmit a first portion of theaggregate input bit stream, and the fixed-rate optical transceiver wouldbe needed to transmit the second portion of the aggregate input bitstream.

For a network built with similar fiber, and using similar opticalequipment throughout, the most common reason for having to lower thetransmittable payload bit rate may be because the second optical path islonger than the first optical path. A longer distance path typicallyrequires additional optical amplification, leading directly to a lowerOSNR.

The simplest rate-adaptive optical transceiver is one that has only twoconfigurable transmittable payload bit rates. In one embodiment of arate-adaptive optical transceiver with two configurable transmittablepayload bit rates, the first transmittable payload bit rate is at leastequal to twice the second transmittable payload bit rate.

The fixed-rate optical transceiver may have a third transmittablepayload bit rate. The third transmittable payload bit rate will likelybe less than the highest transmittable payload bit rate of therate-adaptive optical transceiver. The third transmittable payload bitrate may be less than the highest transmittable payload bit rate of therate-adaptive optical transceiver, but greater than the lowesttransmittable payload bit rate of the rate-adaptive optical transceiver.The third transmittable payload bit rate may be equal to one of thetransmittable payload bit rates of the rate-adaptive opticaltransceiver. The third transmittable payload bit rate may be equal tothe lowest transmittable payload bit rate of the rate-adaptive opticaltransceiver. The third transmittable payload bit rate may be lower thanthe lowest transmittable payload bit rate of the rate-adaptive opticaltransceiver.

In one embodiment, the rate-adaptive optical transceiver may have twoconfigurable transmittable payload bits rates. Additionally, the firsttransmittable payload bit rate of the rate-adaptive optical transceivermay be twice the rate of its second transmittable payload bit rate.Additionally, the transmittable payload bit rate of the fixed-rateoptical transceiver may be equal to the second transmittable payload bitrate of the rate-adaptive optical transceiver. For this embodiment, whenthe apparatus is transmitting the aggregate input bit stream on thesecond optical path, the rate-adaptive optical transceiver may transporthalf the payload of the aggregate input bit stream, and the fixed-rateoptical transceiver may transport half the payload of the aggregateinput bit stream.

In another embodiment, the rate-adaptive optical transceiver may havefour configurable transmittable payload bits rates. Additionally, thesecond transmittable payload bit rate of the rate-adaptive opticaltransceiver may be three-quarters (0.75) the rate of its firsttransmittable payload bit rate. Additionally, the third transmittablepayload bit rate of the rate-adaptive optical transceiver may be half(0.5) the rate of its first transmittable payload bit rate.Additionally, the fourth transmittable payload bit rate of therate-adaptive optical transceiver may be one-quarter (0.25) the rate ofits first transmittable payload bit rate. Additionally, thetransmittable payload bit rate of the fixed-rate optical transceiver maybe equal to the fourth transmittable payload bit rate of therate-adaptive optical transceiver. For this embodiment, when theapparatus is transmitting the aggregate input bit stream on the secondoptical path, the rate-adaptive optical transceiver may transport ¾ thepayload of the aggregate input bit stream, and the fixed-rate opticaltransceiver may transport ¼ the payload of the aggregate input bitstream.

In one network scenario, the rate-adaptive optical transceiver maytransport the entire aggregate input bit stream over a first opticalpath (using a first transmittable bit rate), but may require more thanone fixed-rate optical transceiver to transport the aggregate input bitstream over a second optical path. For instance, in order to transportthe aggregate input stream over the second optical path, it may requirethe rate-adaptive optical transceiver (operating at a secondtransmittable bit rate) and two fixed-rate optical transceivers (eachoperating at a third transmittable bit rate). Furthermore, all threeoptical signals (from the three optical transceivers) may be routed ondifferent optical paths (such as a second optical path, a third opticalpath, and a fourth optical path). In general, the apparatus may compriseof a group of one or more input ports with an aggregate input bitstream, a rate-adaptive optical transceiver having a first transmittablebit rate and at least a second transmittable bit rate, at least onefixed-rate optical transceiver having a third transmittable bit rate,and a means of transmitting the aggregate input bit stream out of theapparatus on a first optical path and on at least a second optical path,wherein when transmitting the aggregate input bit stream on the firstoptical path, the rate-adaptive optical transceiver is used, and whereinwhen transmitting the aggregate input bit stream on the at least secondoptical path, the rate-adaptive optical transceiver and the at least onefixed-rate optical transceiver are used. The apparatus, furthercomprises a plurality of additional fixed-rate optical transceivers,wherein when transmitting the aggregate input bit stream on the at leastsecond optical path, one or more of the plurality of additionalfixed-rate optical transceivers are additionally used.

A single fixed-rate optical transceiver may be used to protect aplurality of rate-adaptive optical transceivers. This is especiallyrelevant if each of the rate-adaptive transceivers is transporting anoptical signal on different optical paths. FIG. 4 shows the case whereone fixed-rate optical transceiver is used to protect the opticalsignals of k rate-adaptive optical transceivers. When one of therate-adaptive optical transceivers 410 a-c needs to switch to a newoptical path that requires the use of the fixed-optical transceiver 456,the 1-of-k selector 450 is configured to select and forward the signalfrom that rate-adaptive optical transceiver's switch port 421 a-c.

In another embodiment, s number of fixed-rate optical receivers may beused to protect the optical signals of k number of rate-adaptive opticaltransceivers (not shown). In such an embodiment, the group of sfixed-rate optical transceivers is shared amongst the group of krate-adaptive optical transceivers in an s-for-k protection scheme. Inthis scheme, one or more fixed-rate optical transceivers may be used toprotect the optical signals of a given rate-adaptive opticaltransceiver. In order to implement the s-for-k protection scheme, the1-of-k selector 450 would be replaced with an s-for-k selector.

In yet another embodiment, a combination of both fixed-rate adaptiveoptical transceivers and rate-adaptive optical transceivers may be usedto protect a group of rate-adaptive optical transceivers. Whentransitioning to a new optical path, a second rate-adaptive opticaltransceiver may be used in combination with the first rate-adaptivetransceiver for cases where additional bandwidth beyond the bandwidth ofa single rate-adaptive optical transceiver and a single fixed-rateoptical transceiver is required.

FIG. 5 illustrates the receiver (RX) portion of an apparatus forperforming path protection for rate-adaptive optics 500 that would beused in conjunction with the transmitter portion of an apparatus forperforming path protection for rate-adaptive optics 400. The receiver(RX) portion of an apparatus for performing path protection forrate-adaptive optics 500 comprises an optical demultiplexer 530 with asingle network (NW) input optical port 526 and a plurality of outputoptical ports 531 a-d, k number of rate-adaptive optical transceivers510 a-c each having a single optical input port 524 a-c and anelectrical switch input port 521 a-c and a group of p output ports 512 a(shown only on rate-adaptive optical transceiver 510 a), a fixed-rateoptical transceiver 556 with a single optical input port 524 d and asingle electrical output port 555, and a 1-to-k director 550.

Each rate-adaptive optical transceiver 510 a-c further comprises RXoptics 522, a plurality of RX rate processors with a selector 530, anelectrical switch 515, an RX output processor 514, an RX mapper function511, and group of p output ports 512 a (shown only on rate-adaptiveoptical transceiver 510 a). The fixed-rate optical transceiver 556further comprises RX optics 558 and electronics 557.

The receiver portion of the apparatus for performing path protection forrate-adaptive optics 500 performs the reverse functions of thetransmitter portion of the apparatus for performing path protection forrate-adaptive optics 400, and its functional blocks perform functionsthat are substantially the same as those functions described inreference to 230 of FIG. 2. In FIG. 5, a wavelength division multiplexed(WDM) optical signal is received at the apparatus input 526, and isforwarded to the optical demultiplexer 530. The optical demultiplexerdemultiplexes the WDM signal into its individual constituentwavelengths, and forwards each wavelength out of its output ports 531a-d to the input ports 524 a-d of the k rate-adaptive opticaltransceivers 510 a-c and the fixed-rate adaptive transceiver 556. Eachrate-adaptive optical transceiver 510 a-c first converts its inputtedoptical signal to an electrical signal using its RX optics 522, and thenforwards the electrical signal to its rate adaptive processors 530. Therate adaptive processor corresponding the rate and format of thereceived signal is used to further process the received electricalsignal. The electrical signal is then passed onto the switch 515 usingone or more physical transport links. The switch is used to combine thephysical transport links from the RX rate processors 530 with one ormore physical transport links from the switch input port 521 a, andforward the combined links to the RX output processor 514. In anon-protection mode, only physical transport links from the RX rateprocessors 530 are forwarded to the RX output processor 514. Afterperforming any needed processing on the signals inputted to it, the RXoutput processor 514 forwards the resulting composite signal to the RXmapper function 511. The RX mapper function 511 is used to map acomposite signal onto the group of p output ports 512 a. The RX mapperfunction 511 may also be used to perform additional functions such asforward error correction and performance monitoring.

The transmitter portion of the apparatus 400 would reside at the startof an optical path, while the receiver portion of the apparatus 500would reside at the end of an optical path. For example, the transmitterportion of a first apparatus may be used to transmit a bit stream to thereceiver portion of a second apparatus, wherein the first apparatus maybe located in a first optical node within an optical network, and thesecond apparatus may be located in a second optical node within theoptical network. When receiving an optical wavelength containing theentire aggregate input bit stream 423 of a rate-adaptive opticaltransceiver transmitter 410 a, the optical demultiplexer 530 forwardsthe wavelength to a single rate-adaptive optical transceiver (RX) 510 a.This would be the case when the optical signal follows a first opticalpath through an optical network. For this case, the switch port 521 a onthe rate-adaptive optical transceiver 510 a goes unused.

When there is a fault on the first optical path, such that thetransmitter portion of the apparatus 400 forwards the aggregate inputbit stream 423 through the network using a second optical path usingboth a rate-adaptive optical transceiver (TX) 410 a (transporting afirst portion of the aggregate input bit stream 423) and at least onefixed rate optical transceiver 456 (transporting the second portion ofthe aggregate input bit stream 423), the receiver portion of theapparatus 500 will receive two wavelengths carrying the aggregate inputbit stream 423. The optical multiplexer 530 will forward one wavelengthto a rate-adaptive transceiver 510 a (containing a first portion of theaggregate input bit stream 423), and one wavelength to a fixed-ratetransceiver 556 (containing the second portion of the aggregate inputbit stream 423). Both the rate-adaptive transceiver 510 a, and thefixed-rate transceiver 556 will convert their respective receivedwavelengths to electrical format and properly demodulate theirrespective signals. The fixed-rate optical transceiver will forward itssecond portion of the aggregate input bit stream 423 to the 1-to-kdirector 550, which will be configured to forward this signal to therate-adaptive optical transceiver 510 a operating on the first portionof the aggregate input bit stream 423. The rate-adaptive opticalreceiver 510 a will receive the second portion of the aggregate inputbit stream from the 1-to-k director 550 via its switch input port 521 a,and it will combine the second portion of the aggregate input bit streamwith its first portion of the aggregate input bit stream using itsswitch 515. The recombined signal will be further processed by the RXoutput processor and RX mapper function prior to be forwarded to thegroup of p output ports 512 a.

The embodiments of the transmitter portion of the apparatus forperforming path protection for rate-adaptive optics that were previouslydescribed apply to the receiver portion of the apparatus for performingpath protection for rate-adaptive optics. For example, embodiments mayinclude: rate-adaptive optics supporting two or four rates/formats,embodiments with more than one fixed-rate optical transceivers,embodiments wherein the payload bit rates are considered, andembodiments wherein both fixed-rate and rate-adaptive opticaltransceivers are used when a second optical path is used due to a faultwithin the optical network.

Previously described were fault scenarios wherein the first and secondoptical paths began 426 and ended 526 on the same optical fiber of theapparatus. In this case, an apparatus comprising of 400 and 500 could beutilized. A second type of apparatus is one that contains multiplenetwork fiber interfaces. Such an apparatus allows the first and secondoptical paths to begin and end on separate optical fibers. FIG. 6A andFIG. 6B depicts an embodiment 600 of one such apparatus for performingpath protection for rate-adaptive optics.

The apparatus 600 contains a transmitter portion (shown in FIG. 6A), anetwork interface portion (shown in FIG. 6A), and a receiver portion(shown in FIG. 6B). The transmitter portion comprises a group of inputports 412 a, one or more rate-adaptive optical transceivers 410 a-c(which are substantially the same as the rate-adaptive opticaltransceivers described in reference to FIG. 4), at least one fixed-rateoptical transceiver 456 (which is substantially the same as thefixed-rate optical transceiver described in reference to FIG. 4), a1-of-k selector 450 (which is substantially the same as the selectordescribed in reference to FIG. 4), an optical multiplexer 430 (which issubstantially the same as the multiplexer described in reference to FIG.4), and an optical output 426.

The network interface portion of the apparatus 600 comprises awavelength router 668, w−1 network input ports 662 a-b, a transmit inputport 667, a receive output port 672, and w−1 network output ports 670a-b. The wavelength router contains w WDM optical inputs 664 a-c and woptical outputs 698 a-c. Each input port 664 a-c and output port 698 a-cof the wavelength router carries an optical wavelength divisionmultiplexed signal having one or more wavelengths. The wavelength router668 provides the ability to route wavelengths from the inputs of therouter 664 a-c to the outputs of the router 698 a-c. A w by w (or M×N,wherein w=M=N) wavelength selective switch (WSS) could perform thisfunction in an example embodiment. It can be noted, however, that fullconnectivity between every input port and every output port is notrequired. As shown in FIG. 6A, the input and output ports of thewavelength router can be segregated into groups: “In Group A” 665 a, “InGroup B” 665 b, “Out Group A” 675 a, and “Out Group B” 675 b. The thickarrows 661 a-c then indicate the connectivity required between the inputand output ports of the router. Specifically, wavelengths are requiredto be routed from the inputs of “In Group A” 665 a to the outputs of“Out Group B” 675 b, but are not required to be routed from the inputsof “In Group A” 665 a to the outputs of “Out Group A” 675 a. However, ingeneral, wavelengths are required to be routed from “In Group B” 665 bto the outputs “Out Group A” 675 a and to the outputs of “Out Group B”675 b, with the exception that wavelengths from given NW Input i are notrequired to be routed to the corresponding given NW Output i. Therefore,as an example, for a network interface portion containing three networkinputs and three network outputs (w=3), NW Input 1 662 a would berequired to route wavelengths to NW Output 2 (not shown) and to NWOutput 3 (not shown), but not to NW Output 1 670 a.

The receiver portion of the apparatus 600 comprises an opticaldemultiplexer 530 (which is substantially the same as the demultiplexer530 of FIG. 5), one or more rate-adaptive optical transceivers 510 a-c(which are substantially the same as the rate-adaptive opticaltransceivers described in reference to FIG. 5), at least one fixed-rateoptical transceiver 556 (which is substantially the same as thefixed-rate optical transceiver described in reference to FIG. 5), a1-to-k selector 550 (which is substantially the same as the selectordescribed in reference to FIG. 5), an input from the network interfaceportion 693 a, an optical fiber or other optical medium 690 a connectingthe receiver portion of 600 to the network interface portion, and a setof p output ports 512 a.

The wavelength routing function 688 shown in FIG. 6A has w opticalinputs 664 a-c and w optical outputs 698 a-c. Each optical input andoutput signal is a wavelength division multiplexed signal containing oneor more optical wavelengths. The wavelength routing function 688 can beconfigured to route wavelengths from its w input ports to its w outputports.

The apparatus 600 may be deployed within an optical node of an opticalnetwork, wherein the network inputs 662 a-b and network outputs 670 a-bof each apparatus 600 is interconnected to the network inputs 662 a-band network outputs 670 a-b of other apparatuses 600 using fiber opticcables. Examples of such networks are shown in FIG. 7, FIG. 8, and FIG.9, wherein each node may contain at least one apparatus 600. In such adeployment, a wavelength arriving at a network input 662 a-b of a node710 a-j may be routed to a network output 670 a-b, or may be routed toone of the optical transceivers within the receiver portion of theapparatus. For example, the WDM optical signal arriving at NW Input 1662 a may be forwarded to the receiver portion 693 a and to all NWOutputs other than NW Output 1. Alternatively, the routing function 668within the network interface portion of the apparatus may be configuredto either forward a given wavelength it receives on one of its inputs664 a-c to one or more outputs 698 a-c, or it may be configured to notforward a given wavelength it receives on one of its inputs to one ormore outputs 698 a-c (and instead block it from reaching some or alloutputs).

The transmitter portion of the apparatus 600 behaves substantiallysimilar to the transmitter 400, other than the fact that the output 426of the optical multiplexer in apparatus 600 is forwarded to input 664 aof wavelength router 668 via an optical fiber or other optical medium663. Similarly, the receiver portion of the apparatus 600 behavessubstantially similar to the receiver 500, other than the fact that itsinput to its optical demultiplexer is connected to output 698 a of thewavelength routing function 688 via an optical fiber or other opticalmedium 690 a.

The network diagrams 700, 800, and 900 shown in FIG. 7, FIG. 8, and FIG.9 will be used to further illustrate the operation of apparatus 600.

FIG. 7 shows a network diagram 700 consisting of eleven optical nodes710 a-k. Each optical node 710 a-k is interconnected to two or moreother optical nodes via fiber optical cables—represented by the solidlines beginning at one node and ending at another node in FIG. 7. Forexample, node G 710 g is interconnected to node D 710 d via opticalcable 750 a, and is additionally interconnected to node H 710 h viaoptical cable 750 b. Each connection between two adjacent optical nodeswill be referred to as a link segment, and for simplicity, all thelengths of each link segment (and all the optical characteristics ofeach link segment) in the networks 700, 800, and 900 are identical. Eachnetwork node 710 a-k may contain an apparatus 600.

FIG. 7 illustrates the network fault scenario wherein the first andsecond optical paths begin on the same optical fiber. For this case, afirst (transmitter) apparatus 600 is located within optical node A, anda second (receiver) apparatus 600 is located within optical node K. Thefirst optical path 720 a-c begins at node A, traverses through opticalnodes B and C, and ends at node K, as illustrated by the dashed linesegments 720 a-c in FIG. 7. The apparatus 600 within node A launches awavelength carrying an aggregate input signal along the first opticalpath 720 a-c. At some point a fault 740 occurs on the fiber betweennodes B 710 b and C 710 c. In order to route around the fault 740, theapparatus 600 within node A performs any necessary adjustments in orderto steer the wavelength carrying the aggregate input signal to thesecond optical path 730 a-e. In one fault recovery scenario, theapparatus within node A utilizes the same wavelength (frequency) whenfollowing the second optical path, but the rate-adaptive opticaltransceiver is unable transmit the additional distance of the secondoptical path, as the second optical path is longer than the firstoptical path by two link segments. Therefore, adjustments must be madewithin the apparatuses at nodes A 710 a, B 710 b, C, 710 c, E 710 e, F710 f, and K 710 k. First, at the apparatus 600 within node A, byappropriately reconfiguring the switch 415 and the 1-of-k selector 450,a first portion of the aggregate input bit stream 423 may be directed tothe TX Rate Processors & Selector 430, and a second portion of theaggregate input bit stream 423 may be redirected to the fixed-rateoptical transceiver 456. Within the TX Rate Processors & Selector block430, a lower bit rate is chosen for the rate-adaptive opticaltransceiver. Additionally, the wavelength (frequency) from therate-adaptive optical transceiver 410 a may need to be changed in orderto avoid a wavelength conflict on the second optical path. Thefixed-rate optical transceiver utilizes a wavelength that differs fromthat used by the rate-adaptive optical transceiver. The wavelength usedby the rate-adaptive optical transceiver when using the first opticalpath may be referred to as a first wavelength (and its correspondingfrequency—a first frequency), while the wavelength used by therate-adaptive optical transceiver when using the second optical path maybe referred to as a second wavelength (and its corresponding frequency—asecond frequency), wherein often the first wavelength is equal to thesecond wavelength. Additionally, the wavelength used by the fixed-rateoptical transceiver may be referred to as a third wavelength (and itscorresponding frequency—a third frequency), wherein the third wavelength(for optical paths beginning on the same fiber) is always different thanthe second wavelength. The optical mux 430 optically multiplexes thesecond and third wavelengths together and forwards the resulting WDMsignal to the wavelength router 668. Since the first optical path andthe second optical path begin on the same optical fiber (the opticalfiber connecting node A and node B), there is no need to reconfigure thewavelength router 668 within the apparatus 600 of node A 710 a.Therefore, if for example, NW Output 1 connected to the optical fiberconnecting node A and node B, then the first and second wavelengthswould be routed from input 664 a to output 698 b on the wavelengthrouter 668.

Continuing on with the network reconfiguration occurring as a result ofthe fault 740, the apparatus 600 within node B 710 b is configured toreroute the second and third wavelengths (from node A) from the firstoptical path 720 a-c to the second optical path 730 a-e (using itswavelength router 668 contained within the apparatus 600 within node B).The apparatuses 600 within node E 710 e and within node F 710 f areconfigured to route the second and third wavelengths along the secondoptical path 730 a-e. The apparatus 600 within node C 710 c isconfigured to route the second and third wavelengths from node F 710 fto node K 710 k, and to not route the first wavelength from node B 710b. Since the second and third wavelengths arrive on the same opticalfiber as the first wavelength, the apparatus 600 within node K 710 kdoes not need to have its wavelength router reconfigured. The apparatus600 within node K 710 k first de-multiplexes the second and thirdwavelengths using its optical de-mux 530, and then forwards the secondwavelength to the rate-adaptive optical transceiver 510 a, and forwardsthe third wavelength to the fixed rate optical transceiver 556. Therate-adaptive optical transceiver 510 a operates on the first portion ofthe aggregate input stream signal 423, and the fixed-rate opticaltransceiver 556 operates on the second portion of the aggregate inputstream signal 423. The rate-adaptive optical transceiver 510 a convertsthe second optical wavelength to electrical format and demodulates it,and then forwards the first portion of the aggregate input bit stream423 to the electrical switch 515. The fixed-rate optical transceiver 556converts the third optical wavelength to electrical format anddemodulates it, after which it forwards the second portion of theaggregate input bit stream 423 to the 1-to-k director 550. The 1-to-kdirector 550 is configured to forward the signal from the fixed-rateoptical transceiver to the switch 515 of the rate-adaptive opticaltransceiver 510 a that is operating on the second optical wavelength.The switch 515 within 510 a combines the first portion of the aggregateinput bit stream with the second portion of the aggregate input bitstream in order to form the aggregate output bit stream 523, which isthen forwarded to the output ports 512 a.

If the second wavelength is equal to the first wavelength, then acolored optical de-multiplexer may be used for de-mux 530. If the secondwavelength is different from the first wavelength, then a colorlessoptical de-multiplexer may be used for de-mux 530. A colored opticalde-multiplexer operates such that a given physical output is coupled toa specific wavelength, whereas with a colorless optical de-multiplexer agiven physical output may be used for any wavelength within a range ofwavelengths. An example of a colored optical de-multiplexer is anarrayed waveguide grating (AWG), while an example of a colorless opticalde-multiplexer is a 1-to-w optical coupler followed by an array of woptical tunable filters.

FIG. 8 depicts the scenario wherein the first optical path 720 a-cbegins on a first optical fiber 850 a, and the second optical path 830a-e begins on a second optical fiber 850 b. FIG. 8 shows a networkdiagram 800 consisting of eleven optical nodes 710 a-k. Each opticalnode 710 a-k is interconnected to two or more other optical nodes viafiber optical cables—represented by the solid lines beginning at onenode and ending at another node in FIG. 8. In 800, each fiber connectionbetween two adjacent optical nodes will be referred to as a linksegment, and for simplicity, all the lengths of each link segment (andall the optical characteristics of each link segment) in the network 800are identical. Each network node 710 a-k may contain an apparatus 600.

FIG. 8 illustrates the network fault scenario wherein the first andsecond optical paths begin on two different optical fibers (fibers 850 aand 850 b). For this case, a first (transmitter) apparatus 600 islocated within optical node A 710 a, and a second (receiver) apparatus600 is located within optical node K 710 k. The first optical path 720a-c begins at node A 710 a, traverses through optical nodes B 710 b andC 710 c, and ends at node K 710 k, as illustrated by the dashed linesegments 720 a-c in FIG. 7. The apparatus 600 within node A 710 alaunches a wavelength carrying an aggregate input signal along the firstoptical path 720 a-c. At some point a fault 840 occurs on the fiberbetween nodes A 710 a and B 710 b. In order to route around the fault840, the apparatus 600 within node A 710 a performs the necessaryadjustments in order to steer the wavelength carrying the aggregateinput signal to the second optical path 830 a-e. In one fault recoveryscenario, the apparatus within node A utilizes the same wavelength(frequency) when following the second optical path, but therate-adaptive optical transceiver is unable transmit the additionaldistance of the second optical path, as the second optical path islonger than the first optical path by two link segments. Therefore,adjustments must be made within the apparatuses at nodes A 710 a, D 710d, E 710 e, F 710 f, C 710 c, and K 710 k. First, at the apparatus 600within node A, by appropriately reconfiguring the switch 415 (within 410a) and the 1-of-k selector 450, a first portion of the aggregate inputbit stream 423 may be directed to the TX Rate Processors & Selector 430(within 410 a), and a second portion of the aggregate input bit stream423 may be redirected to the fixed-rate optical transceiver 456. Withinthe TX Rate Processors & Selector block 430 (within 410 a), a lower bitrate is chosen for the rate-adaptive optical transceiver 410 a.Additionally, the optical wavelength from the rate-adaptive opticaltransceiver may need to be changed in order to avoid a wavelengthconflict on the second optical path. The fixed-rate optical transceiverutilizes a wavelength that differs from that used by the rate-adaptiveoptical transceiver. The wavelength used by the rate-adaptive opticaltransceiver when using the first optical path may be referred to as afirst wavelength (and its corresponding frequency—a first frequency),while the wavelength used by the rate-adaptive optical transceiver whenusing the second optical path may be referred to as a second wavelength(and its corresponding frequency—a second frequency), wherein often thefirst wavelength is equal to the second wavelength. Additionally, thewavelength used by the fixed-rate optical transceiver may be referred toas a third wavelength (and its corresponding frequency—a thirdfrequency), wherein the third wavelength is always different than thesecond wavelength. The optical mux 430 optically multiplexes the secondand third wavelengths together and forwards the resulting WDM signal tothe wavelength router 668. Since the first optical path and the secondoptical path begin on different optical fibers (the optical fiberconnecting node A and node B 850 a, and the optical fiber connectingnode A to node D 850 b), there is a need to reconfigure the wavelengthrouter 668 within the apparatus 600 of node A 710 a. For example, if NWOutput 1 670 a is connected to the optical fiber connecting node A andnode B 850 a, and if NW Output w 670 b is connected to the optical fiberconnecting node A and node D 850 b, then the first wavelength would berouted from input 664 a to output 698 b within the wavelength router,and the second and third wavelengths would be routed from input 664 a tooutput 698 c within the wavelength router.

Continuing on with the network reconfiguration occurring as a result ofthe fault 840, the apparatuses 600 within node D 710 d, node E 710 e,and node F 710 f are configured to route the second and thirdwavelengths along the second optical path 830 a-e. The apparatus 600within node C 710 c is configured to route the second and thirdwavelengths from node F 710 f to node K 710 k, and to not route thefirst wavelength from node B 710 b. Since the second and thirdwavelengths arrive on the same optical fiber as the first wavelength,the apparatus 600 within node K 710 k does not need to have itswavelength router reconfigured. The apparatus 600 within node K 710 kfirst de-multiplexes the second and third wavelengths using the opticalde-mux 530, and then forwards the second wavelength to the rate-adaptiveoptical transceiver 510 a, and forwards the third wavelength to thefixed-rate optical transceiver 556. The rate-adaptive opticaltransceiver 510 a operates on the first portion of the aggregate inputstream signal 423, and the fixed-rate optical transceiver 556 operateson the second portion of the aggregate input stream signal 423. Therate-adaptive optical transceiver 510 a converts the second opticalwavelength to electrical format and demodulates it, after which it isforwarded to the switch 415. The fixed-rate optical transceiver 556converts the third optical wavelength to electrical format anddemodulates it, after which it is forwarded to the 1-to-k director 550.The 1-to-k director 550 is configured to forward the signal from thefixed-rate optical transceiver to the switch 515 of the rate-adaptiveoptical transceiver 510 a that is operating on the second opticalwavelength. The switch 515 within 510 a combines the first portion ofthe aggregate input bit stream with the second portion of the aggregateinput bit stream in order to form the aggregate output bit stream 523,which is then forwarded to the output ports 512 a.

If the second and third wavelengths arrived at Node K 710 k via adifferent optical fiber—from node J 710 j for example—then thewavelength router 668 within node K 710 j would need to be reconfigured.For instance, assume that the first optical path arrived at node K 710 kon NW Input 1 662 a, and that the second optical path arrived at node K710 k on NW Input w 662 b. Then, before the fault 840, the wavelengthrouter 668 within the apparatus 600 of node K 701 k would be configuredto route the first wavelength from input 664 b of the wavelength router668 to output 698 a of the router 668, while after the fault 840, thewavelength router 668 within the apparatus 600 of node K 710 k would beconfigured to route the second and third wavelengths from input 664 c ofthe wavelength router 668 to output 698 a of the router 668.

Another network example that can be examined is depicted in FIG. 9. FIG.9 shows a network diagram 900 consisting of eleven optical nodes 710a-k. Each optical node 710 a-k is interconnected to two or more otheroptical nodes via fiber optical cables—represented by the solid linesbeginning at one node and ending at another node in FIG. 9. Eachconnection between two adjacent optical nodes will be referred to as alink segment, and for simplicity, all the lengths of each link segment(and all the optical characteristics of each link segment) in thenetwork 900 are identical. Each network node 710 a-k may contain anapparatus 600.

The network 900 is used to illustrate the concept of fixed-rate opticaltransceiver protection sharing. In 900, prior to any network faults,three optical paths are established using three different rate-adaptiveoptical transceivers within the apparatus 600 within node E 710 e. Morespecifically, a first optical path 920 using a first wavelength and afirst rate-adaptive optical transceiver 410 a is established betweennode E 710 e and node B 710 b, and a second optical path 930 using asecond wavelength and a second rate-adaptive optical transceiver 410 bis established between node E 710 e and node D 710 d, and a thirdoptical path 950 using a third wavelength and a third rate-adaptiveoptical transceiver 410 c is established between node E 710 e and node F710 f. The first 410 a, second 410 b, and third 410 c rate-adaptiveoptical transceivers within optical node E 710 e are protected by asingle fixed-rate optical transceiver 456 within the apparatus 600within node E 710 e. This assumes that there is only a single fiberfault in the network 900 at any given point in time. With respect tonetwork 900, assume that a given rate-adaptive transceiver is only ableto transport the entire input aggregate bit rate when the distance isonly two or fewer optical links.

Assume now that a fault 940 a occurs on the fiber between Node E 710 eand Node B 710 that affects the first wavelength generated by the firstrate-adaptive optical transceiver 410 a. For this fault case, at node E710 e, the data within the first wavelength now will be redirected suchthat it follows the fourth optical path 925 a-c. In order to do this,the apparatus 600 within node E 710 e performs the necessary adjustmentsin order to steer the wavelength carrying the aggregate input signal tothe second optical path 925 a-c. First, at 410 a within the apparatus600 within node E 710 e, by appropriately reconfiguring the switch 415and the 1-of-k selector 450, a first portion of the aggregate input bitstream 423 may be directed to the TX Rate Processors & Selector 430, anda second portion of the aggregate input bit stream 423 may be redirectedto the fixed-rate optical transceiver 456. For this fault (940 a), the1-of-k selector 450 is configured to forward the electrical signal atinput 452 a of the selector to output 454 of the selector. Thewavelength used by the first rate-adaptive optical transceiver whenusing the fourth optical path may be referred to as the fourthwavelength, while the wavelength used by the fixed-rate opticaltransceiver may be referred to as the fifth wavelength. The optical mux430 optically multiplexes the fourth and fifth wavelengths together andforwards the resulting WDM signal to the wavelength router 668. Sincethe first optical path and the fourth optical path begin on differentoptical fibers (the optical fiber connecting node E and node B, and theoptical fiber connecting node E 710 e to node F 710 f), there is a needto reconfigure the wavelength router 668 within the apparatus 600 ofnode E 710 e. For example, if NW Output 1 670 a connected to the opticalfiber connecting node E 710 e and node B 710 b, and if NW Output w 670 bconnected to the optical fiber connecting node E 710 e and node F 710 f,then the first wavelength would be routed from input 664 a to output 698b within the wavelength router, and the fourth and fifth wavelengthswould be routed from input 664 a to output 698 c within the wavelengthrouter.

Assume now that prior to any other faults, a fault 940 b occurs on thefiber between Node E 710 e and Node D 710 d that affects the secondwavelength generated by the second rate-adaptive optical transceiver 410b. For this case, at node E 710 e, the data within the second wavelengthnow will now be redirected to follow the fifth optical path 935 a-c. Inorder to do this, the apparatus 600 within node E 710 e performs thenecessary adjustments in order to steer the wavelength carrying theaggregate input signal to the fifth optical path 935 a-c. First, at 410b within the apparatus 600 within node E 710 e, by appropriatelyreconfiguring the switch and the 1-of-k selector within 410 b, a firstportion of the aggregate input bit stream of 410 b may be directed tothe TX Rate Processors & Selector of 410 b, and a second portion of theaggregate input bit stream may be redirected to the fixed-rate opticaltransceiver 456. For this fault (940 b), the 1-of-k selector 450 isconfigured to forward the electrical signal at input 452 b of theselector to output 454 of the selector. The wavelength used by thesecond rate-adaptive optical transceiver 410 b when using the fifthoptical path may be referred to as the sixth wavelength, while thewavelength used by the fixed-rate optical transceiver 456 may bereferred to as the fifth wavelength. The optical mux 430 opticallymultiplexes the sixth and fifth wavelengths together and forwards theresulting WDM signal to the wavelength router 668. Since the secondoptical path and the fifth optical path begin on different opticalfibers (the optical fiber connecting node E 710 e and node D 710 d, andthe optical fiber connecting node E 710 e to node B 710 b), there is aneed to reconfigure the wavelength router 668 within the apparatus 600of node E 710 e. For example, if NW Output 1 670 a is connected to theoptical fiber connecting node E 710 e and node D 710 d, and if NW Outputw 670 b is connected to the optical fiber connecting node E 710 e andnode B 710 b, then the second wavelength would be routed from input 664a to output 698 b on the wavelength router 668, and the sixth and fifthwavelengths would be routed from input 664 a to output 698 c on thewavelength router 668.

Assume now that prior to any other faults, a fault 940 c occurs on thefiber between Node E 710 e and Node F 710 f that affects the thirdwavelength generated by the third rate-adaptive optical transceiver 410c. For this case, at node E 710 e, the data within the third wavelengthnow will be redirected to follow the sixth optical path 955 a-d. Inorder to do this, the apparatus 600 within node E 710 e performs thenecessary adjustments in order to steer the wavelength carrying theaggregate input signal to the sixth optical path 955 a-d. First, at 410c within the apparatus 600 within node E 710 e, by appropriatelyreconfiguring the switch and the 1-of-k selector within 410 c, a firstportion of the aggregate input bit stream of 410 c may be directed tothe TX Rate Processors & Selector of 410 c, and a second portion of theaggregate input bit stream may be redirected to the fixed-rate opticaltransceiver 456. For this fault (940 c), the 1-of-k selector 450 isconfigured to forward the electrical signal at input 452 c of theselector to output 454 of the selector. The wavelength used by the thirdrate-adaptive optical transceiver when using the sixth optical path maybe referred to as the seventh wavelength, while the wavelength used bythe fixed-rate optical transceiver may be referred to as the fifthwavelength. The optical mux 430 optically multiplexes the seventh andfifth wavelengths together and forwards the resulting WDM signal to thewavelength router 668. Since the third optical path and the sixthoptical path begin on different optical fibers (the optical fiberconnecting node E 710 e and node F 710 f, and the optical fiberconnecting node E 710 e to node D 710 d), there is a need to reconfigurethe wavelength router 668 within the apparatus 600 of node E 710 e. Forexample, if NW Output 1 670 a is connected to the optical fiberconnecting node E 710 e and node F 710 f, and if NW Output w 670 bconnected to the optical fiber connecting node E 710 e and node D 710 d,then the third wavelength would be routed from input 664 a to output 698b within the wavelength router 668, and the seventh and fifthwavelengths would be routed from input 664 a to output 698 c within thewavelength router 668.

Assuming that the optical paths in the network 900 are bidirectionalpaths, the receiver portion of the apparatus 600 may protect the receiveportions of the three rate-adaptive optical transceivers 510 a-c. Thisis accomplished by the apparatus 600 in node E710 e in the followingmanner. When the two wavelengths arrive at the wavelength router 668,the router 668 is configured to route both wavelengths (the one from therate-adaptive optical transceiver, and one from the fixed-rate opticaltransceiver within the apparatus 600 within the far-end node) to theoptical de-multiplexer 526 within the apparatus 600 within node E 710 e.Based upon the two wavelengths used by the far-end node, the opticalde-multiplexer 526 forwards one wavelength to the appropriaterate-adaptive optical transceiver 510 a-c and one wavelength to thefixed-rate optical transceiver 556. As long as there is only one faultassociated with the three optical paths associated with the threerate-adaptive optical transceivers, the single fixed-rate opticaltransceiver 556—in combination with other circuitry within apparatus600—may protect all three optical paths in the receive direction. In oneembodiment the fixed-rate optical transceiver uses a specific wavelengthregardless of which rate-adaptive optical transceiver path is beingprotected. For this case, a colored optical de-multiplexer 530 can beutilized with the apparatus 600. In another embodiment the fixed-rateoptical transceiver may use any available wavelength. For this case, atleast the drop port 531 d to the fixed-rate optical transceiver must becolorless. In another embodiment, the drop ports 531 a-c to therate-adaptive optical transceivers may colored drop ports, while thedrop port to the fixed-rate optical transceiver may be colorless.

From the above three fault scenarios 940 a-c it can be seen that onefixed-rate optical transceiver in combination with the other circuitrywithin apparatus 600 can protect up to w rate-adaptive opticaltransceivers under a single network fault scenario, assuming that eachrate-adaptive optical transceiver is operating on a separate networkoptical fiber. Additional fixed-rate optical transceivers may bedeployed within the apparatus 600 in order to provide coverage for twoor more simultaneous faults within the network. Such a protection schemewould provide s number of fix-rate protection transceivers for every knumber of rate-adaptive optical transceivers (s for k protection).

From the diagrams 600, 700, 800, and 900—and the associated discussionfor these diagrams—an apparatus, comprising: a group of one or moreinput ports with an aggregate input bit stream, a rate-adaptive opticaltransceiver having a first transmittable bit rate and at least a secondtransmittable bit rate, at least one fixed-rate optical transceiverhaving a third transmittable bit rate, and a means of transmitting theaggregate input bit stream out of the apparatus on a first optical pathand on at least a second optical path may be constructed. The apparatusis such that when transmitting the aggregate input bit stream on thefirst optical path, the rate-adaptive optical transceiver is used, andwherein when transmitting the aggregate input bit stream on the at leastsecond optical path, the rate-adaptive optical transceiver and the atleast one fixed-rate optical transceiver are used. The apparatus mayfurther comprise of a first output port connected to a first opticalfiber, and a second output port connected to a second optical fiber,wherein the first optical path begins on the first optical fiber and theat least second optical path begins on the second optical fiber. Theapparatus may further comprise of a means for moving the rate-adaptiveoptical transceiver from the first output port to the second outputport.

The means of transmitting the aggregate input bit stream out of theapparatus on a first optical path and on at least a second optical pathis provided by the rate-adaptive optical transceiver 410 a with aninternal switch 415 (and a corresponding switch port 421 a), a 1-of-kselector 450, at least one fixed-rate optical transceiver 456, andoptical multiplexer 430, and a wavelength router 668.

The means of means for moving the rate-adaptive optical transceiver fromthe first output port (port 698 b, for example) to the second outputport (port 698 c, for example) is provided by the wavelength router 668.

There may be instances wherein the rate-adaptive optical transceiver anda single fixed-rate optical transceiver are unable to transport theentire aggregate input bit stream on certain optical paths. For thesecases, the apparatus 600 may further comprise of a plurality ofadditional fixed-rate optical transceivers, wherein when transmittingthe aggregate input bit stream on the at least second optical path, oneor more of the plurality of additional fixed-rate optical transceiversare additionally used. For example, suppose that a rate-adaptive opticaltransceiver transports a 30 Gbps bit stream on a first optical path, andit is only able to transport a 10 Gbps bit stream on a second opticalpath. Also suppose a given fixed-rate optical transceiver is only ableto transport 10 Gbps on the second optical path. Then when transportingthe 30 Gbps on the second optical path, the rate-adaptive opticaltransceiver and two fixed-rate optical transceivers are required. Inorder to enable this embodiment, the 1-of-k selector 450 and the 1-to-kdirector 550 should be replaced with k-by-s and s-by-k electricalswitches respectively. For the k-by-s switch that replaces 450, eachinput 452 a-c of the switch would be connected to a switch output port421 a-c on one of the k rate-adaptive optical transceivers 410 a-cwithin the apparatus 600, and each output of the switch would beconnected to one of the s fixed-rate optical transceivers 456 within theapparatus 600. For the s-by-k switch that replaces 550, each output 552of the switch would be connected to a switch input port 521 a-c on oneof the k rate-adaptive optical transceivers 510 a-c within the apparatus600, and each input 554 of the switch would be connected to one of the sfixed-rate optical transceivers 556 within the apparatus 600. Ingeneral, a single bidirectional k-by-s electrical switch may be used inplace of the k-by-s and s-by-k electrical switches. Alternatively, asingle n-by-n bidirectional electrical switch may bee used in place ofthe k-by-s and s-by-k electrical switches, wherein n is equal to thehigher number of either the rate-adaptive optical transceivers orfixed-rate optical transceivers within the apparatus 600. When using thesingle n-by-n bidirectional electrical switch, some number of inputs andoutputs on the switch may likely not be used.

With respect to the network fault scenario described in regard tonetwork 900, an apparatus can be described that has the ability to sharea fixed-rate optical transceiver between at least two rate-adaptiveoptical transceivers. The apparatus, comprises a first group of one ormore input ports with an aggregate input bit stream, a firstrate-adaptive optical transceiver having a first transmittable bit rateand at least a second transmittable bit rate, at least one fixed-rateoptical transceiver having a third transmittable bit rate, and a meansof transmitting the aggregate input bit stream out of the apparatus on afirst optical path and on at least a second optical path. The apparatusis such that when transmitting the aggregate input bit stream on thefirst optical path, the rate-adaptive optical transceiver is used, andwherein when transmitting the aggregate input bit stream on the at leastsecond optical path, the rate-adaptive optical transceiver and the atleast one fixed-rate optical transceiver are used. The apparatus furthercomprises a second group of one or more input ports having a secondaggregate input bit stream, a second rate-adaptive optical transceiverhaving the first transmittable bit rate and at least the secondtransmittable bit rate, and a means of transmitting the second aggregateinput bit stream out of the apparatus on a third optical path and on atleast a fourth optical path, wherein when transmitting the secondaggregate input bit stream on the third optical path, the secondrate-adaptive optical transceiver is used, and wherein when transmittingthe second aggregate input bit stream on the at least fourth opticalpath, the second rate-adaptive optical transceiver and the at least onefixed-rate optical transceiver are used. The apparatus 600 furthercomprises a first output port connected to a first optical fiber; and asecond output port connected to a second optical fiber, wherein thefirst optical path begins on the first optical fiber, and the thirdoptical path begins on the second optical fiber.

In addition to its transmitter functionally, the apparatus 600 may alsobe described in terms of its receiver functionally. The apparatus 600,comprises one or more optical input ports 662 a-b used to input anaggregate bit stream, a rate-adaptive optical transceiver 510 a thatreceives at a first receivable bit rate and at least a second receivablebit rate, at least one fixed-rate optical transceiver 556 that receivesat a third receivable bit rate, and a means of receiving the aggregatebit stream from a first optical path and from at least a second opticalpath. When the apparatus 600 is receiving the aggregate bit stream fromthe first optical path, the rate-adaptive optical transceiver is used,and when the apparatus 600 is receiving the aggregate bit stream fromthe at least second optical path, the rate-adaptive optical transceiverand the at least one fixed-rate optical transceiver are used. Theaggregate bit stream may be received from the at least second opticalpath as a result of a fault on the first optical path.

When receiving the aggregate bit stream from the first optical path, therate-adaptive optical transceiver 510 a receives the aggregate bitstream at the first receivable bit rate, and when receiving theaggregate bit stream from the second optical path, the rate-adaptiveoptical transceiver receives the aggregate bit stream at the secondreceivable bit rate.

In one network scenario, the first optical path may be shorter that theat least second optical path. In such a scenario, the rate-adaptiveoptical transceiver may be unable to transport the entire aggregate bitstream over the second optical path, thereby requiring the assistance ofthe fixed-rate optical transceiver when the second optical path is usedfor transmission.

In one embodiment of the apparatus 600, the first receivable bit rate isgreater than the second receivable bit rate. In another embodiment ofthe apparatus, the first receivable bit rate is at least equal to twicethe second receivable bit rate. In another embodiment of the apparatus600, the second receivable bit rate is about equal to the thirdreceivable bit rate.

An optical fiber may be connected to one of the one or more opticalinput ports 662 a-b, and the first optical path and the at least secondoptical path may terminate (end) on the optical fiber. Alternatively,the one or more optical input ports 662 a-b may include a first opticalinput port connected to a first optical fiber, and a second opticalinput port connected to a second optical fiber. For this configuration,the first optical path may terminate (end) on the first optical fiberand the at least second optical path may terminate (end) on the secondoptical fiber. The apparatus 600 may further comprise a means of movingthe rate-adaptive optical transceiver from the first optical fiber tothe second optical fiber. This means may be in the form of a wavelengthrouter 668.

The apparatus 600 may further comprise a plurality of additionalfixed-rate optical transceivers, wherein when receiving the aggregatebit stream on the at least second optical path, one or more of theplurality of additional fixed-rate optical transceivers may additionallybe used.

The apparatus 600 may additionally comprise a second rate-adaptiveoptical transceiver 510 b having the first receivable bit rate and atleast the second receivable bit rate, and a means of receiving a secondaggregate bit stream from a third optical path and from at least afourth optical path, wherein when receiving the second aggregate bitstream from the third optical path, the second rate-adaptive opticaltransceiver 510 b is used, and wherein when receiving the secondaggregate bit stream from the at least fourth optical path, the secondrate-adaptive optical transceiver 510 b and the at least one fixed-rateoptical transceiver 556 are used. It can be noted that since thefixed-rate optical transceiver 556 is used with both the rate-adaptiveoptical transceiver 510 a and the second rate-adaptive opticaltransceiver 510 b, in order to protect against all single fiber faultswith an optical network, the first optical path and the third opticalpath should not share any fiber links. Therefore, the one or moreoptical input ports may include a first optical input port connected toa first optical fiber, and a second optical input port connected to asecond optical fiber, wherein the first optical path terminates on thefirst optical fiber, and the third optical path terminates on the secondoptical fiber.

Based upon the previous descriptions, a method for preforming pathprotection may be defined. The method comprises first receiving anaggregate input bit stream at the transmitting apparatus 600 (such as423 shown in FIG. 6A), and then transmitting the aggregate input bitstream using a rate-adaptive optical transceiver (such as 410 a in FIG.6A) when transmitting on a first optical path (such as 720 a-c in FIG.7), and transmitting the aggregate input bit stream using therate-adaptive optical transceiver (such as 410 a in FIG. 6A) and afixed-rate optical transceiver (such as 456 in FIG. 6A) whentransmitting on a second optical path (such as 730 a-e in FIG. 7)following a fault (such as 740 in FIG. 7) on the first optical path.When transmitting the aggregate input bit stream on the first opticalpath, the rate-adaptive optical transceiver may transmit using a firsttransmittable bit rate, and when transmitting the aggregate input bitstream on the second optical path, the rate-adaptive optical transceivermay transmit using a second transmittable bit rate, wherein the firsttransmittable bit rate may be greater than the second transmittable bitrate. Furthermore, the transmittable bit rate of the fixed-rate opticaltransceiver may be equal to the second transmittable bit rate of therate-adaptive optical transceiver. Additionally, the first transmittablebit rate may be at least equal to twice the second transmittable bitrate. Also, according to the method, the first optical path may beshorter than the at least second optical path. Additionally, the firstoptical path and the second optical path may begin on a first opticalfiber (such as the optical paths 720 a and 730 a shown in FIG. 7).Alternatively, the first optical path may begin on a first optical fiberand the second optical path may begin on a second optical fiber (such asoptical paths 720 a-c and 830 a-e shown in FIG. 8).

The method also comprises moving the rate-adaptive optical transceiverfrom the first optical fiber to the second optical fiber after the faulton the first optical path. Such a scenario is depicted in FIG. 8involving the fault 840. When fault 840 occurs, the wavelength router668 within apparatus 600 is reconfigured in order to forward theaggregate input bit stream from a first network output 670 a to a secondnetwork output 670 b.

The method additionally comprises utilizing one or more additionalfixed-rate optical transceivers when transporting the aggregate inputbit stream on the second optical path. One or more additional fixed-rateoptical transceivers may be used when the rate-adaptive opticaltransceiver and a single fixed-rate optical transceiver do not haveenough bandwidth to transport the aggregate input bit stream on thesecond optical path.

The method further comprises receiving a second aggregate input bitstream, transmitting the second aggregate input bit stream using asecond rate-adaptive optical transceiver when transmitting on a thirdoptical path, and transmitting the second aggregate input bit streamusing the second rate-adaptive optical transceiver and the fixed-rateoptical transceiver when transmitting on a fourth optical path followinga fault on the third optical path. For this case, the first optical pathmay begin on a first optical fiber and the third optical path may beginon a second optical fiber, since one fixed-rate optical transceiver isused to protect the first optical path of two rate-adaptive opticaltransceivers, as depicted in reference to the network scenarios shown inFIG. 9.

At the receiving apparatus 600, the method comprises first receiving anaggregate bit stream. This may be the aggregate input bit stream 423 sodescribed with reference to the transmitting apparatus. The aggregatebit stream may be received from a single optical fiber (such as a fiberconnected to NW Input 1 662 a, for example), or it may be received frommore than one optical fiber (such as fibers connected to NW Input 1 662a and NW Input w 662 b, for example). The aggregate bit stream may bereceived from a single optical wavelength, or from a plurality ofoptical wavelengths. The method further comprises forwarding theaggregate bit stream using a rate-adaptive optical transceiver (like 510a) when receiving from a first optical path, and forwarding theaggregate bit stream using the rate-adaptive optical transceiver and afixed-rate optical transceiver (like 556) when receiving from a secondoptical path following a fault on the first optical path. Two possibleoptical paths between two apparatuses within two optical nodes areillustrated in FIG. 7 (720 a-c and 730 a-e), wherein a transmittingapparatus 600 may be located in node A 710 a, and wherein a receivingapparatus 600 may be located in node K 710 k. For the network faultscenario shown in FIG. 7, the aggregate bit stream is received from asingle fiber both before and after the fault 740. Before the fault 740,the aggregate bit stream is received from the first optical path 720 a-cusing a single optical wavelength. After the fault 740, the aggregatebit stream is received from the first second path 730 a-e using twooptical wavelengths (one for the rate-adaptive optical transceiver, andone for the fixed-rate optical transceiver). When receiving theaggregate bit stream from the first optical path, the rate-adaptiveoptical transceiver may receive at a first receivable bit rate, and whenreceiving the aggregate bit stream from the second optical path, therate-adaptive optical transceiver may receive at a second receivable bitrate, wherein the first receivable bit rate may be greater than thesecond receivable bit rate. Additionally, when receiving the aggregatebit stream from the second optical path, the receivable bit rate of thefixed-rate optical transceiver may be equal to the second receivable bitrate of the rate-adaptive optical transceiver. Alternatively, whenreceiving the aggregate bit stream from the first optical path, therate-adaptive optical transceiver may receive at a first receivable bitrate, and when receiving the aggregate bit stream from the secondoptical path, the rate-adaptive optical transceiver may receive at asecond receivable bit rate, wherein the first receivable bit rate may beat least equal to twice the second receivable bit rate. Furthermore,when receiving the aggregate bit stream from the first and secondoptical paths, the first optical path may be shorter than the secondoptical path.

Additionally, when receiving the aggregate bit stream, the first opticalpath and the second optical path may terminate (end) on a first opticalfiber at the receiver apparatus 600 (as illustrated in FIG. 7).Alternatively, when receiving the aggregate bit stream, the firstoptical path may terminate (end) on a first optical fiber and the secondoptical path may terminate (end) on a second optical fiber. (This isillustrated by the two optical paths 920 and 925 a-c in FIG. 9.). Themethod further comprises moving the rate-adaptive optical transceiverfrom the first optical fiber to the second optical fiber after the faulton the first optical path. (This was done by the wavelength router 668within node B 710 b following the fault 940 a in FIG. 9. The wavelengthrouter 668 routes a wavelength from the second optical path (from thesecond fiber) to the rate-adaptive optical transceiver 510 a, therebyeffectively moving the rate-adaptive optical transceiver 510 a from thefirst fiber to the second fiber.)

The method further comprises using one or more of a plurality ofadditional fixed-rate optical transceivers when receiving the aggregatebit stream on the second optical path. This may be done when therate-adaptive optical transceiver 510 a and a single fixed-rate opticaltransceiver 556 are unable to provide enough bandwidth to receive theaggregate bit stream.

The method additionally comprises receiving a second aggregate bitstream, forwarding the second aggregate bit stream using a secondrate-adaptive optical transceiver when receiving from a third opticalpath, and forwarding the second aggregate bit stream using the secondrate-adaptive optical transceiver and the fixed-rate optical transceiverwhen receiving from a fourth optical path following a fault on the thirdoptical path. When using the fixed-rate optical transceiver to protectthe paths of both the first aggregate bit stream and the secondaggregate bit stream, the paths may not share any common links (opticalfibers). For this case, when receiving the aggregate bit stream from thefirst optical path, the first optical path terminates on a first opticalfiber, and when receiving the second aggregate bit stream from the thirdoptical path the third optical path terminates on a second opticalfiber.

An optical node may include the entirety of apparatus 600. For thiscase, the optical node comprises a group of one or more input ports withan aggregate input bit stream, a rate-adaptive optical transceiverhaving a first transmittable bit rate and at least a secondtransmittable bit rate, at least one fixed-rate optical transceiverhaving a third transmittable bit rate, and a means of transmitting theaggregate input bit stream from the optical node on a first optical pathand on at least a second optical path, wherein when transmitting theaggregate input bit stream on the first optical path, the rate-adaptiveoptical transceiver is used, and wherein when transmitting the aggregateinput bit stream on the at least second optical path, the rate-adaptiveoptical transceiver and the at least one fixed-rate optical transceiverare used. The optical node may transmit the aggregate input bit streamon the at least second optical path as a result of a fault on the firstoptical path.

The optical node may transmit the aggregate input bit stream on thefirst optical path with the rate-adaptive optical transceiver using afirst transmittable bit rate, and may transmit the aggregate input bitstream on the second optical path with the rate-adaptive opticaltransceiver using a second transmittable bit rate. Furthermore, thefirst transmittable bit rate may be greater than the secondtransmittable bit rate. Alternatively, the first transmittable bit rateis at least equal to twice the second transmittable bit rate. Also, thesecond transmittable bit rate may be about equal to the thirdtransmittable bit rate.

The optical node may further comprise an output port connected to anoptical fiber, wherein the first optical path and the at least secondoptical path begin on the optical fiber.

The optical node may further comprise a first output port connected to afirst optical fiber, and a second output port connected to a secondoptical fiber, wherein the first optical path begins on the firstoptical fiber and the at least second optical path begins on the secondoptical fiber. Additionally, the optical node may further comprise ameans for moving the rate-adaptive optical transceiver from the firstoutput port to the second output port.

The optical node may further comprise a plurality of additionalfixed-rate optical transceivers, wherein when transmitting the aggregateinput bit stream on the at least second optical path, one or more of theplurality of additional fixed-rate optical transceivers are additionallyused.

The optical node may additionally comprise a second group of one or moreinput ports having a second aggregate input bit stream, a secondrate-adaptive optical transceiver having the first transmittable bitrate and at least the second transmittable bit rate, and a means oftransmitting the second aggregate input bit stream out of the apparatuson a third optical path and on at least a fourth optical path, whereinwhen transmitting the second aggregate input bit stream on the thirdoptical path, the second rate-adaptive optical transceiver is used, andwherein when transmitting the second aggregate input bit stream on theat least fourth optical path, the second rate-adaptive opticaltransceiver and the at least one fixed-rate optical transceiver areused.

The optical node may further comprise a first output port connected to afirst optical fiber, and a second output port connected to a secondoptical fiber, wherein the first optical path begins on the firstoptical fiber, and the third optical path begins on the second opticalfiber.

A plurality of network nodes containing the apparatus 600 may beinterconnected to form an optical network. The optical network maycomprise a first optical node and at least a second optical node, andthere exists a first optical path and at least a second optical pathconnecting the first optical node and the at least second optical node.The first optical node may comprise a group of one or more input portswith an aggregate bit stream, a rate-adaptive optical transceiver havinga first transmittable bit rate and at least a second transmittable bitrate, and at least one fixed-rate optical transceiver having a thirdtransmittable bit rate.

The first optical node may transmit the aggregate bit stream to the atleast second optical node over the first optical path using therate-adaptive optical transceiver, and the first optical node maytransmit the aggregate bit stream to the at least second optical nodeover the second optical path using the rate-adaptive optical transceiverand the at least one fixed rate optical transceiver. The first opticalnode may transmit the aggregate bit stream over the at least secondoptical path as a result of a fault on the first optical path.

When the aggregate bit stream is transmitted over the first optical pathbetween the first optical node and the at least second optical node, therate-adaptive optical transceiver may transmit with the firsttransmittable bit rate, and when transmitting the aggregate bit streamover the second optical path between the first optical node and the atleast second optical node, the rate-adaptive optical transceiver maytransmit with the second transmittable bit rate.

In one network, the first optical path is shorter than the at leastsecond optical path.

The first transmittable bit rate of the first optical node within theoptical network may be greater than the second transmittable bit rate.The first transmittable bit rate of the first optical node within theoptical network may be at least equal to twice the second transmittablebit rate. The second transmittable bit rate of the first optical nodewithin the optical network may be about equal to the third transmittablebit rate of the first optical node within the optical network.

The first optical node may further comprise an output port connected toan optical fiber, wherein the first optical path and the at least secondoptical path begin on the optical fiber. Alternatively, the firstoptical node may additionally comprise a first output port connected toa first optical fiber, and a second output port connected to a secondoptical fiber, wherein the first optical path begins on the firstoptical fiber and the at least second optical path begins on the secondoptical fiber. Additionally, the first optical node may comprise a meansfor moving the rate-adaptive optical transceiver from the first outputport to the second output port.

The first optical node may further comprise additional fixed-rateoptical transceivers, wherein when transmitting the aggregate bit streamover the at least second optical path, one or more of the plurality ofadditional fixed-rate optical transceivers may be additionally used.

The first optical node may further comprise a second group of one ormore input ports having a second aggregate bit stream, a secondrate-adaptive optical transceiver having the first transmittable bitrate and at least the second transmittable bit rate, and a means oftransmitting the second aggregate bit stream from the first optical nodeover a third optical path and over at least a fourth optical path,wherein when transmitting the second aggregate bit stream over the thirdoptical path, the second rate-adaptive optical transceiver is used, andwherein when transmitting the second aggregate bit stream over the atleast fourth optical path, the second rate-adaptive optical transceiverand the at least one fixed-rate optical transceiver are used. The firstoptical node may additionally comprise of a first output port connectedto a first optical fiber, and a second output port connected to a secondoptical fiber, wherein the first optical path begins on the firstoptical fiber, and the third optical path begins on the second opticalfiber.

The second optical node in the optical network may further comprise asecond rate-adaptive optical transceiver receiving at a first receivablebit rate and at least a second receivable bit rate, at least oneadditional fixed-rate optical transceiver receiving at a thirdreceivable bit rate. When receiving the aggregate bit stream from thefirst optical path at the second optical node, the second rate-adaptiveoptical transceiver within the second optical node is used, and whereinwhen receiving the aggregate bit stream from the at least second opticalpath at the second optical node, the second rate-adaptive opticaltransceiver within the second optical node and the at least oneadditional fixed-rate optical transceiver within the second optical nodeare used. The aggregate bit stream may be received at the second opticalnode from the at least second optical path as a result of a fault on thefirst optical path. When receiving the aggregate bit stream from thefirst optical path, the second rate-adaptive optical transceiver withinthe second optical node receives at the first receivable bit rate, andwherein when receiving the aggregate bit stream from the second opticalpath, the second rate-adaptive optical transceiver within the secondoptical node receives at the second receivable bit rate. The firstreceivable bit rate at the second optical node may be greater than thesecond receivable bit rate. Additionally, the first receivable bit rateat the second optical node may be at least equal to twice the secondreceivable bit rate. Also, the second receivable bit rate at the secondoptical node may be about equal to the third receivable bit rate.Additionally, the first receivable bit rate is equal to the firsttransmittable bit rate, and the second receivable bit rate is equal tothe second transmittable bit rate, and the third receivable bit rate isequal to the third transmittable bit rate.

In the foregoing description, the invention is described with referenceto specific example embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the present invention.The specification and drawings are accordingly to be regarded in anillustrative rather than restrictive sense.

What is claimed is:
 1. An apparatus, comprising: a rate-adaptive opticaltransceiver having a first receivable bit rate and at least a secondreceivable bit rate; at least one fixed-rate optical transceiver havinga third receivable bit rate; and a means of receiving an aggregate bitstream from a first optical path and from at least a second opticalpath, wherein when receiving the aggregate bit stream from the firstoptical path, the rate-adaptive optical transceiver receiving with thefirst receivable bit rate is used, and wherein when receiving theaggregate bit stream from the at least a second optical path, therate-adaptive optical transceiver receiving with the at least a secondreceivable bit rate and the at least one fixed-rate optical transceiverare used.
 2. The apparatus of claim 1, wherein the aggregate bit streamis received from the at least a second optical path as a result of afault on the first optical path.
 3. The apparatus of claim 1, whereinthe first optical path is shorter than the at least a second opticalpath.
 4. The apparatus of claim 1, wherein the first receivable bit rateis greater than the at least a second receivable bit rate.
 5. Theapparatus of claim 1, wherein the first receivable bit rate is at leastequal to twice the at least a second receivable bit rate.
 6. Theapparatus of claim 1, wherein the at least a second receivable bit rateis about equal to the third receivable bit rate.
 7. The apparatus ofclaim 1, further comprising an optical fiber, wherein the first opticalpath and the at least a second optical path terminate on the opticalfiber.
 8. The apparatus of claim 1, further comprising a first opticalfiber and a second optical fiber, wherein the first optical pathterminates on the first optical fiber and the at least a second opticalpath terminates on the second optical fiber.
 9. The apparatus of claim8, further comprising a means for moving the rate-adaptive opticaltransceiver from the first optical fiber to the second optical fiber.10. The apparatus of claim 1, further comprising a plurality ofadditional fixed-rate optical transceivers, wherein when receiving theaggregate bit stream from the at least a second optical path, one ormore of the plurality of additional fixed-rate optical transceivers areadditionally used.
 11. The apparatus of claim 1, further comprising: asecond rate-adaptive optical transceiver having the first receivable bitrate and the at least a second receivable bit rate; and a means ofreceiving a second aggregate bit stream from a third optical path andfrom at least a fourth optical path, wherein when receiving the secondaggregate bit stream from the third optical path, the secondrate-adaptive optical transceiver is used, and wherein when receivingthe second aggregate bit stream from the at least a fourth optical path,the second rate-adaptive optical transceiver and the at least onefixed-rate optical transceiver are used.
 12. The apparatus of claim 11,further comprising a first optical fiber and a second optical fiber,wherein the first optical path terminates on the first optical fiber andthe third optical path terminates on the second optical fiber.
 13. Anapparatus, comprising: a group of one or more input ports having anaggregate input bit stream; a rate-adaptive optical transceivertransmitting using a first wavelength and a second wavelength; at leastone fixed-rate optical transceiver transmitting using a thirdwavelength; and a means of transmitting the aggregate input bit streamon a first optical path and on at least a second optical path, whereinwhen transmitting the aggregate input bit stream on the first opticalpath, the aggregate input bit stream is transmitted by the rate-adaptiveoptical transceiver using the first wavelength, and wherein whentransmitting the aggregate input bit stream on the second optical path,the aggregate input bit stream is transmitted by the rate-adaptiveoptical transceiver using the second wavelength and by the at least onefixed-rate optical transceiver.
 14. The apparatus of claim 13, whereinwhen transmitting on the first optical path the rate-adaptive opticaltransceiver transmits using a first transmittable bit rate, and whereinwhen transmitting on the at least a second optical path therate-adaptive optical transceiver transmits using a second transmittablebit rate, wherein the second transmittable bit rate is less than thefirst transmittable bit rate.
 15. The apparatus of claim 13, wherein thefirst wavelength is equal to the second wavelength.
 16. The apparatus ofclaim 13, wherein a wavelength router is the means of transmitting theaggregate input bit stream on the first optical path and on the at leasta second optical path.
 17. The apparatus of claim 13, wherein the thirdwavelength is multiplexed with the second wavelength.
 18. A method forperforming path protection, comprising: receiving an aggregate input bitstream comprising of a first portion and a second portion; transmittingthe first portion and the second portion using a first opticaltransceiver when transmitting on a first optical path; and transmittingthe first portion on a second optical path using the first opticaltransceiver following a fault on the first optical path, andtransmitting the second portion on a third optical path using a secondoptical transceiver following the fault on the first optical path,wherein when transmitting the first portion and the second portion onthe first optical path, the first optical transceiver transmits using afirst transmittable bit rate, and wherein when transmitting the firstportion and not the second portion on the second optical path, the firstoptical transceiver transmits using a second transmittable bit rate,wherein the first transmittable bit rate is greater than the secondtransmittable bit rate.
 19. The method of claim 18, wherein the secondoptical path and the third optical path are the same optical path. 20.The method of claim 18, wherein the first optical transceiver is arate-adaptive optical transceiver, and wherein the second opticaltransceiver is a fixed-rate optical transceiver.
 21. The method of claim18, further comprising: receiving the first portion and the secondportion using a third optical transceiver when receiving from the firstoptical path; and receiving the first portion from the second opticalpath using the third optical transceiver following the fault on thefirst optical path, and receiving the second portion from the thirdoptical path using a fourth optical transceiver following the fault onthe first optical path, wherein when receiving the first portion and thesecond portion from the first optical path, the third opticaltransceiver receives at the first transmittable bit rate, and whereinwhen receiving the first portion from the second optical path, the thirdoptical transceiver receives at the second transmittable bit rate.